improving microwave capacity
DESCRIPTION
We explain how to improve microwave radio capacity by understanding techniques that improve throughput.TRANSCRIPT
1
UNDERSTANDING TECHNIQUES TO IMPROVE THROUGHPUT
AVIAT ADVANCED MICROWAVE TECHNOLOGY SEMINAR IMPROVING MICROWAVE CAPACITY
is just a big pipe
you get out what you put in
microwave
“I canna change the laws o’ physics captain”
How to Understand Vendor Capacity Claims?
• It is getting increasingly harder to compare capacity claims from various vendors
• Multiple techniques are being employed to boost throughput figures
• We will attempt to explain the various techniques and how they impact capacity
APRIL 2012 4 AVIAT NETWORKS |
How can you get more data through the pipe?
NOVEMBER 2011 5 AVIAT NETWORKS |
through the pipe? how do you get more data
Strategies for Increasing Microwave Capacities
More Spectral Efficiency
(More Bits per Hz)
More Spectrum (More Hz)
More “Effec5ve” Throughput
(More Data per Bit)
Technique
Higher Modula6on Levels
Adap6ve Modula6on
Reduced FEC Redundancy
Technique
Header Op6miza6on/ Suppression/Compression
Payload Compression
Asymmetric Opera6on
APRIL 2012 AVIAT NETWORKS | 6
Technique
Wider Channels
Mul6ple channels with link aggrega6on (incl. CCDP)
Get a Bigger Pipe!
NOVEMBER 2011 7 AVIAT NETWORKS |
How can you get more data through the pipe? get a bigger pipe!
Use Wider Channels
6 GHz
30 MHz
60 GHz
250 MHz
70-90 GHz
5 GHz
11 GHz
40 MHz
18 GHz
80 MHz 23 GHz
50 MHz
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NOVEMBER 2011 9 AVIAT NETWORKS |
Get a Bigger Pipe! How can you get more data through the pipe? use more efficient schemes to pack more data into the pipe
Increasing Modulation Level
þ Improves bits/Hz efficiency within the same channel size
☒ Diminishing capacity improvement with every higher modulation step
☒ Much lower system gain - shorter hops, larger antennas
☒ Much higher sensitivity to interference – difficult link coordination, reduced link density
☒ Increased phase noise and linearity – increased design complexity cost
þ Should be deployed with ACM to offset lower system gain
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Modula6on Level (QAM)
Bits/Symbol Bits/s/Hz
Incremental Capacity Gain
4 (QPSK) 2 -‐
8 3 50%
16 4 33%
32 5 25%
64 6 20%
128 7 17%
256 8 14%
512 9 13%
1024 10 11%
2048 11 10%
Higher Modulation = More Capacity, but…
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8QA
M
16Q
AM
32Q
AM
64Q
AM
128Q
AM
256Q
AM
512Q
AM
1024
QA
M
2048
QA
M
10%
15%
20%
25%
30%
35%
40%
45%
50%
55%
Cap
acity
Incr
ease
45
40
35
30
25
20
15
10
5
0 Car
rier t
o In
terf
eren
ce R
atio
(C/I)
, dB
110
105
100
95
90
85
80
75
70
65
Syst
em G
ain,
dB
Applying Adaptive Modulation
• AM/ACM allows higher order modulations to be employed, but mitigate the adverse effects
• Modulation rate/capacity adapts to increase system gain when needed
• Fixed modulation links can be upgraded to ACM to: 1. Increase link capacity 2. Decrease antenna size, and so tower rental costs 3. Increase link availability 4. Or, a combination of 1+2+3
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Forward Error Correction (FEC)
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PAYLOAD FEC
Typical Radio Frame NMS
Bytes reserved for radio link and network
management informa6on
FEC bytes enable radio to correct a limited number of
bit errors, increasing receiver performance
Forward Error Correction
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PAYLOAD FEC
Typical Radio Frame NMS
PAYLOAD FEC NMS
‘Light’ FEC
Increased Payload = Higher Throughput
Less FEC = Decreased System Gain
‘Strong’ Forward Error Correction
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PAYLOAD FEC
Typical Radio Frame NMS
PAYLOAD FEC NMS
PAYLOAD FEC NMS
‘Light’ FEC
‘Strong’ FEC
Decreased Payload = Lower Throughput
More FEC = Beaer System
Gain
Use more than one pipe
NOVEMBER 2011 16 AVIAT NETWORKS |
use more than one pipe
Link Aggregation using IEEE 802.1AX
• The most common legacy link aggregation approach (originally defined in IEEE 802.3ad)
• 802.1AX cannot dynamically redistribute traffic load for optimal utilization of available links
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Switch/Router
Mod
ule
Mod
ule
Eclipse INU/INUe
DAC GE3
P3 DPP1
DPP2 P5
DAC GE3
DPP1
DPP2
RAC 60
P4
P3
P5
P4
RAC 60
RAC 60
RAC 60
P1
P2
P3
P4
P5
P6
Eclipse INU/INUe
DAC GE3
P3 DPP1
DPP2 P5
DAC GE3
DPP1
DPP2
RAC 60
P4
P3
P5
P4
RAC 60
RAC 60
RAC 60
Switch/Router
Mod
ule P1
P2
P3
Mod
ule P4
P5
P6
4+0 Link
CCDP/XPIC or
ACAP
LAG
Designed for this
Supports this
Layer 1 Link Aggregation (L1 LA)
• Unique and Aviat patented radio link aggregation scheme designed to address limitations of the traditional 802.1AX approach
• Uniform load balancing even for ACM links and carriers of different capacities • High utilization and low added overhead • Carrier-grade convergence and recovery from individual link failures (<50 msec)
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Switch/Router
Mod
ule
Mod
ule
Eclipse INU/INUe
DAC GE3
P3 DPP1
DPP2 P5
DAC GE3
DPP1
DPP2
RAC 60
P4
P3
P5
P4
RAC 60
RAC 60
RAC 60
P1
P2
P3
P4
P5
P6
Eclipse INU/INUe
DAC GE3
P3 DPP1
DPP2 P5
DAC GE3
DPP1
DPP2
RAC 60
P4
P3
P5
P4
RAC 60
RAC 60
RAC 60
Switch/Router
Mod
ule P1
P2
P3
Mod
ule P4
P5
P6
4+0 Link
L1LA Domain Layer 2 (802.1AX) Domain
LAG
LAG
Sta
ckin
g
Comparing Link Aggregation Options
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LAG 802.1AX L1 LA
Load balancing Effec6veness Medium High
Easy capacity expansion Yes Yes
Latency High Low
Adap6ve to RF No Yes
L1LA is the ideal solution for N+0 links
Only send the data that you need through the pipe
NOVEMBER 2011 20 AVIAT NETWORKS | through the pipe
only send the data that you need
Using Ethernet Optimization
• Using common Ethernet optimization and compression techniques: • Ethernet Frame Suppression • MAC Header Compression • Multi-Layer Header Compression • Payload Compression
• Send only needed data over the radio link. Suppress or compress everything else
• Asymmetric link operation
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Ethernet Frame Header Optimization
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!
• Inter-frame Gap and Preamble Removal
• MAC Header Compression
Throughput Improvement
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Header Suppression Throughput Improvement
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Frame Size
Standard Frame IFG & Preamble IFG & Preamble & MAC header
Frame Space Mbps Frame
Space Mbps Increase Frame Space Mbps Increase
64 84 76.2 68 94.1 24% 58 110.3 45%
128 148 86.5 132 97.0 12% 122 104.9 21%
260 280 92.9 264 98.5 6% 254 102.4 10%
512 522 96.2 516 99.2 3% 506 101.2 5%
1518 1538 98.7 1522 99.7 1% 1512 100.4 2%
Multi-Layer Header Compression
• AKA ‘Packet Throughput Boost’, ‘Enhanced Packet Compression’ ‘Layer 1/2/3/4 Header Compression’ or ‘Deep Ethernet header compression’
• Adds compression of IPv4/v6 header address bytes • Still highly dependent upon payload traffic type and frame size
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Payload Compression
• Some microwave vendors are employing common compression techniques
• Pros • Replaces strings of repeated patterns of data
• Promises dramatic throughput improvement (2.5x), with no additional spectrum requirement
• Cons • Improvement is not guaranteed nor predictable, since it is highly
dependent on the traffic mix
• Increased link latency
• Most data traffic is already compressed
• Typical real-world improvement is minimal (~4%)
• Payload compression has not been generally adopted in the industry
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Asymmetric Link Operation
• Proposal to configure links with lower capacity upstream than downstream
• Assumes downstream traffic is much higher volume than upstream, and that backhaul links can be similarly dimensioned
• Claimed benefits are higher downstream speeds and frequency savings (upstream)
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IN CONCLUSION
Beware common tactics to inflate throughput
• Present throughput figures based upon 64 byte frame sizes only
• Assume that up to 100% (or a large proportion) of traffic is compressible
• Assume availability of very wide channels (80 MHz) • Assume 2+0 co-channel operation on the same frequency
assignment (using XPIC) • Present half-duplex throughput figures • Include non-payload overhead (NMS, FEC) • Assume gains from other unproven techniques
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When it comes to Microwave Capacity
Test, using an industry standard benchmark - RFC 2544
Best Case Throughput – 80 MHz channel
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340
Airlink Strong FEC
360
IFG+PA Suppression
450
MAC HC
520
2+0 XPIC
1040
Payload Compression
2000
1024QAM
2500
360 360
720 720* 900
‘Guaranteed’ throughput
Maximum ‘Best Efforts’ throughput 64 byte frame size, ideal traffic profile
Throughput figures are stated in Mbit/s and are approximate for a single 80MHz RF channel and 256QAM (unless otherwise stated)
* + Latency
Realistic Throughput – 30 MHz channel
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180
Airlink Strong FEC
190
IFG+PA Suppression
201
MAC HC
209
2+0 XPIC
418
Payload Compression
435
1024QAM
544
190 190 380 380*
475
‘Guaranteed’ throughput
Maximum throughput For 260 bytes average frame sizes, and typical traffic profile
Throughput figures are stated in Mbit/s and are approximate for a single 30MHz RF channel and 256QAM (unless otherwise stated)
* + Latency
+4%
+6% +4%
+25%
Capacity Improvements – Hype and Availability
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Hype Factor Availability Higher Modula6on Medium 6-‐12 months
Strong FEC Low Now
ACM Low Now
Aggregated Mul6-‐Channel Low Now
Traffic Op6miza6on High Now
Payload Compression High Now
Asymmetrical Opera6on High ??
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